This application relates to a roof system for a building. It relates particularly to a roof system with an outer coating which is applied to a building roof substrate (e.g. a roof deck, in the case of an original roof, or an existing roof which is being recovered). The coating is applied on top of the roof substrate in a fluid form, and dries in air to a monolithic sheet of rubber-like material which resists leakage, and protects the roof's substrates from ambient conditions.
Roof systems for commercial, industrial or institutional buildings can be adversely affected by a condition known as thermal stress. Thermal stress is a condition caused by expansion and contraction of the different components of the roof system due to varying ambient temperatures. The different components of the roof system have different coefficients of expansion, so that they expand and contract to different degrees as the ambient temperature varies. When components of a roof system are subjected to varying temperature conditions, the expansion and contraction of the roof's components often causes cracks to form in the roof system, particularly in the system's outer coating. When cracks form in the system, it allows moisture to penetrate, eventually resulting in leakage, and other serious problems for the roof system.
An old and well known technique for forming a roof on a building is to build up a multiple ply system on top of a roof deck. The system is built up with alternating layers of (i) asphalt or tar, and (ii) paper felts. However, there are several problems which are involved in forming such a roof system. If the asphalt or tar is applied hot, as is common, it poses safety hazards. Specifically, it can cause severe burns to the people who work with it. It can also cause fires. Further, it creates dangerous fumes. Also, the system is relatively rigid, and has virtually no elasticity to accommodate movement of components of the building. When the components of such a system are subjected to thermal stress, the system often exhibits the type of cracking discussed above. Still further, when an asphalt or tar based coating is used, it is customary to cover the coating with gravel, or other solids, in order to protect it from ambient conditions. This adds considerable weight to the roof system, which is not desirable.
More recently, there has been developed what is known as a "one-ply" roofing material and process. Pre-formed sheets of rubber-like material are laid on top of the roof substrate, and are adhered to the roof substrate either by (i) bonding the sheets to the entire roof substrate by means of adhesives, or (ii) bonding the perimeters of the sheets to the roof substrate with adhesive, and depositing large specially shaped pieces of gravel or stone on top of the sheets to help hold them in place. An advantage of this system over the multi-ply, built-up roof system is that the single-ply sheet material can stretch in order to accommodate movement of the components of the building due to thermal stress, settling, etc., to resist the formation of cracks.
However, the applicant believes that there are still significant problems involved in the one-ply system. First of all, it is virtually always necessary to use several sheets of the material in order to cover a roof. Because of the fact that several sheets are used, it is necessary to bond the adjacent edges of the sheets to each other. This creates seams, which are the weakest points in the system and are the primary points where leakage can occur, unless great skill is exercised in bonding the sheets to each other. Still further, in those systems where large specially formed pieces of gravel or stones are used to help hold the sheets in place, the gravel and stones add considerable weight to the roof system.
Further, during the course of development of this invention, a possible fluid roof system was suggested to the applicant by Rohm & Haas, a manufacturer of one of the polymeric emulsions used in the preferred form of the applicant's system. It was suggested that a coating could be formed by adding solids and liquids to that manufacturer's particular polymeric emulsion. In the composition suggested by the supplier, the total solids (polymeric and non-polymeric) constituted about 69% (by weight) of the coating. The polymeric solids constituted about 22% of the coating, and the non-polymeric solids constituted about 46% of the coating. From the applicant's experience, such a coating is undesirable because of the relatively small percentage of polymeric solids, and the relatively high percentage of non-polymeric solids. The coating is more water absorbent than the applicant believes a roof coating should be. Further, the coating has less tear strength, and elongation capability than what the applicant believes a roof coating should have. Additionally, the coating lacks the adhesion capability which the applicant was looking for in a roof coating.